Device for testing ionization smoke detector

ABSTRACT

A testing device for an ionization smoke detector having series connected opened and closed ionization chambers and means for detecting a change of impedance of the open chamber wherein means are employed to generate a variable voltage which is applied to the open ionization chamber to produce a change in voltage across the ionization chamber corresponding to that produced by a change in smoke concentration and means for interrupting the variation in voltage immediately upon operation of the detector to determine the sensitivity of the detector to the presence of smoke.

United States Patent Sasaki et al. [451 Apr. 18, 1972 DEVICE FOR TESTING IONIZATION Re rences Cited SMOKE DETECTOR UNITED STATES PATENTS [721 lnvemm W" Y Kttbayaski, 3,235,858 2/1966 Mader "340/237 s Ful'sawa Japan i 3,500,368 3/1970 Abe .540/237-5 [73] Assignee: Nittan Company, Limited, Tokyo, Japan Primary Examiner-John W. Caldwell [22] Wed May 1970 Assistant Examiner-Daniel Myer PP 39,329 Attorney-Eugene E. Geoffrey, Jr.

[30] Foreign Application Priority Data ABSTRACT June 2, 1969 Japan ..44/4256 A testing device for an ionization smoke detector having series June 2, 1969 Japan... ..44/75975 connected opened and closed ionization chambers and means Sept. ll, 1969 Japan... ..44/71586 for detecting a change of impedance of the open chamber Sept. 1], 1969 Japan ..44/78974 wherein means are employed to generate a variable voltage which is applied to the open ionization chamber to produce a g zggg gf g change in voltage across the ionization chamber correspond- [58} Field or sli r iiw ...........'.'3'li' 7i 1,' lie, 41 1, 237 s; 1 that by a change Smke and 250/435 D, 44, 836 FT means for interrupting the variation in voltage immediately upon operation of the detector to determine the sensitivity of the detector to the presence of smoke.

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Patented A ril 18, 1972 3,657,713

Y [I To 40 of FIGS 2 a 3 y ,3

l /2 6| i-Q I 34... 23 i H70 .50 of FIGS 25 3 2, I7 I ro so of F165 28 3 Powm SUPPLY 1; 1 I A 42 POWER 1: SUPPLY 1. i:'\ 63 56 txwavrrms Aouu SflSflK/ DEVICE FOR TESTING IONIZATION SMOKE DETECTOR This invention relates to a testing device for ionization smoke detectors and more specifically to a novel and improved device for making operational and sensitivity tests on ionization smoke detectors which donot requireactual exposure of the detector to predetermined smoke concentrations.

Prior testing procedures for ionization smoke detectors have involved the actual exposure of the detector to smoke of selected concentrations to determine not only operability of tors which will enable the performance of operational and sen-' sitivity tests utilizing electrical circuitry to apply electrical signals correspondingv precisely to the electrical signals produced by the smoke detector as the smoke concentration increases.

The ionization smoke detector to be tested by a device in accordance with the invention includes a closed ionization chamber, an open ionization chamber, a field efiect transistor for detecting a voltage change appearing at the junction of the ionization chambers when the smoke enters the open chamber and a relay driven by the field effect transistor. The testing device in accordance with the invention generates a variable voltage which is utilized to change the voltage at the junction of the ionization chambers. An indicator indicates the mag nitude of the output voltage produced by the generator and means are provided for interrupting the change of voltage in response to operation of the relay forming part of the ionization smoke generator.

The above and other objects of the invention will become more apparent from the following description and accompanying drawings forming part of this application.

in the drawings: 7

FIG. 1 is a circuit diagram illustrating one form of ionization detector to be tested by apparatus in accordance with the invention;

FIG. 2 is a circuit diagram of one embodiment of testing apparatus in accordance with the invention; and

FIG. 3 is a circuit diagram of another embodiment of testing apparatus in accordance with the invention.

An ionization smoke detector to be tested by apparatus in accordance with the invention is shown in FIG. 1. The detector includes a closed ionization chamber having a pair of electrodes 1 1 and 12 having a radioactive source 13. The open ionization chamber denoted by the numeral 20 similarly includes a pair of electrodes 21 and 22 and a radioactive source 23. The electrode 11 of the chamber 10 is connected to a positive conductor 4 while the electrode 21 of the chamber 20 is connected to a switching arm 16 of a single pole double throw switch 15. The electrodes 12 and 22 of the chambers are connected together at the junction 1. One fixed contact 17 of the switch is connected to a negative conductor 5 while the second fixed contact 18 is connected to the conductor 6 to which a test voltage is applied. The junction 1 of the two chambers is connected to the gate electrode G of the field effect transistor 3. The source S of the field effect transistor is connected through a resistor 31 to the conductor 5 while the drain electrode D is connected directly to the conductor 4. A silicon controlled rectifier (SCR) 7 serves as a switching device and is connected between the conductors 4 and 5. The control electrode of the SCR is connected through a zener diode 8 to the source electrode of the field effect transistor 3. in normal operation of the ionization detector described above. the arm 16 of switch 15 is moved into contact with the contact 17. When smoke enters the chamber 20, .the impedance of that chamber increases, and this in turn increases the voltage at the junction 1. This increased voltage causes the field effect transistor to conduct and will therefore raise the voltage at the source electrode. When the voltage of the source electrode exceeds the voltage of the zener diode 8, the latter will conduct and supply a control signal to the control electrode of the SCR 7. The SCR 7 then, becomes conducting and short circuits the conductors 4 and 5 causing the transmission of a signal to an alarm device which may be interconnected with the conductors 4 and 5. In order to test the operation of the smoke detector, the open ionization chamber 20 must be exposed to smoke as in the case of fire. As previously mentioned, this procedure is very difficult as the rate of increase of smoke concentration must be carefully and accu-. rately controlled and such procedure is diificult if not impossible to attain.

One embodiment of an improved testing device in accordance with the invention is illustrated in FIG. 2. In this embodiment a constant voltage source 25 energizes a variable generating circuit 26, the latter producing a slowly increasing voltage at the output terminals. A relay 28 is energized when the smoke detector under test operates to produce an alarm. An indicator 29 indicates the output voltage of the variable voltage generating circuit 26. The output terminals 40, 50, and 60 of the testing device are connected, respectively, to the terminals 4, 5, and 6 of the detector as shown in FIG. 1.

The variable voltage generating circuit 26 has a positive transistor 53 is connected to the positive conductor 35 while the source electrode is connected to the base electrode of a transistor 54. The collector of transistor 54'is connected to the positive conductor 35 while the emitter is connected through a load resistor 55 to the conductor 37. The test voltage terminal 60 is connected to the emitter of transistor 54 and an indicator '29 is connected in parallel with the load resistor 55.

A control switch 57 is connected in parallel with a capacitor 52 of the time constant circuit. This switch is mechanically interlocked with a second switch 58 connected in series with the coil 43 of the relay 28. The switches are arranged so that when switch 58 is closed, the switch 57 will be open and vice versa. The relay 28 includes a second pair of contacts 42 connected in series with the lamp 56 across the conductors 35 and 37.

In testing an ionization smoke detector such as that shown.

in FIG. 1, the switch 15 is operated to move the switch arm 16 to the contact 18 and the conductors 4, 5, and 6 are connected, respectively, to the terminals 40, 50, and 60. The switch 57 is open and the switch 58 is closed.

At the start of the test, the relay contacts 41 of the relay 28 are closed since the relay 28 is not energized. Under these conditions capacitor 52 will be charged at a predetermined rate. In the present instance the time constant of the time constant circuit is adjusted so that it will be greater than the time constant of the ionization detector under test. The increase of voltage across the capacitor 52 results in a change of impedance of the field effect transistor 53. This impedance change is converted into a voltage change by the transistor 54 and the voltage of the emitter will slowly increase. The emitter voltage of transistor 54 appears at the test voltage terminal 60. Inasmuch as the voltage of the electrode 21 of the ionization chamber 20 is increased by reason of its connection to the ter- 3 plied by the terminal 60."o f the testing device to the detector electrode 21 increases, a voltage change is thereby produced at the gate of the field effect transistor 3 in the same manner as if smoke were emitted to the ionization chamber 20.

When the voltage applied to the'conductor 6 increases to a level causing the SCR 7 to conduct, the relay 28 is actuated and causes the contacts 41 to open and the contacts 42 to close.0pening of the contacts 41 immediately interrupts the application of a change to the capacitor 52 and the second contact 42 illuminates the lamp 56 to provide an indication that the ionization detector has operated. Inasmuch as the input impedance of the field effect transistor 53 is relatively high, the charge on the capacitor 52 at the moment the contact 41 is opened will remain for a short period. Accordingly, the voltage at terminal 60 will also be maintained constant for a short period so that the magnitude of the voltage can be determined by the indicator 29 and thereby afford a direct indication of the sensitivity of the smoke detector.

After the magnitude of the voltage has been determined by reading the indicator 29, the switch 58 is opened and the switch 57 is closed, the latter functioning to immediately discharge the capacitor 52 and cause the voltage of the capacitor to return to zero. The testing device can now be connected to another ionization smoke detector and the test is initiated by opening the switch 57 and closing the switch 58.

A modified embodiment of the invention is illustrated in FIG. 3 and corresponding components of FIGS. 2 and 3 have been denoted by like numerals. ln'this embodiment of the invention the time constant circuit for producing the variable voltage includes a current limiting resistor 61, the sourcedrain path of the field effect transistor 62, relay contacts 41 and a capacitor 52 connected in series between the conductors 35 and 37. The gate electrode of the field effect transistor 62 is connected to a movable arm 65 of a potentiometer '64. The resistance element of the potentiometer 64 is connected in series with a resistor 63 between the conductors 35 and 37. As in the case of the previous embodiment of the invention, it is desirable to select a time constant which is greater than the time constant of the ionization chambers of the detector under test. With this configuration of a time constant circuit, the source potential of transistor 62 will vary in response to the current flowing through the resistor 61 while the gate voltage will be maintained at a fixed level as determined by the position of the movable arm 65 on the potentiometer 64. Thus the source-drain path of the field effect transistor 62 functions as a constant current circuit as long as the voltage at the gate 65 is fixed. This arrangement causes the voltage to change across the capacitor 52 to be substantially linear with respect to time. Since the voltage at the output terminal 60 is controlled by the voltage across the capacitor 52, the voltage at the terminal 60 linearly, and this operation improves the ease and accuracy of making measurements and in the adjustment of the operation of the smoke detector under test. This modified embodiment of the invention also enables the charging rate of the capacitor 52 to be controlled by adjusting the movable contactor 65 on the potentiometer 64 to modify 'the potential of the gate of field effect transistor 62. v

While only certain embodiments of the invention have been illustrated and described, it is apparent that alterations, modifications and changes may be made without departing from the true scope and spirit thereof pended claims.

We claim:

. l. A testing device for an ionization smoke detector having a pair of terminals for connection to a power source, an open ionization chamber, a closed ionization chamber, a pair of electrodes in each of said chambers with said pairs of electrodes being connected in series circuit between said pair of terminals for application of a voltage thereto, means including afield effect transistor interconnected with said chamber electrodes for detecting a voltage across at least one chamber and producing an output voltage proportional thereto, and a relay interconnected with said transistor and actuated in res use to an output voltage of predetermined magmtude, said comprising a generator for producing a variable voltage connected to said terminals, said generator including a time constant circuit controlling the rate of change of said variable voltage, means interconnected with said generator and relay and operable in response to actuation of said relay to interrupt further change of said variable voltage and maintain it at the magnitude attained at the moment said relay is actuated and means for indicatingthe magnitude of said variable voltage.

2. A testing device for an ionization smoke detector according to claim 1 wherein said time constant circuit includes a field effect transistor and a capacitor connected in series with the source-drain path thereof and across said voltage supply, the gate of the last said transistor being connected to a reference voltage.

3. A testing'device for an ionization smoke detector according to claim 2 wherein the time constant of said time constant circuit is greater than the time constant of said ionization chamber circuit.

as defined by the ap- CVICC 

1. A testing device for an ionization smoke detector having a pair of terminals for connection to a power source, an open ionization chamber, a closed ionization chamber, a pair of electrodes in each of said chambers with said pairs of electrodes being connected in series circuit between said pair of terminals for application of a voltage thereto, means including a field effect transistor interconnected with said chamber electrodes for detecting a voltage across at least one chamber and producing an output voltage proportional thereto, and a relay interconnected with said transistor and actuated in response to an output voltage of predetermined magnitude, said device comprising a generator for producing a variable voltage connected to said terminals, said generator including a time constant circuit controlling the rate of change of said variable voltage, means interconnected with said generator and relay and operable in response to actuation of said relay to interrupt further change of said variable voltage and maintain it at the magnitude attained at the moment said relay is actuated and means for indicating the magnitude of said variable voltage.
 2. A testing device for an ionization smoke detector according to claim 1 wherein said time constant circuit includes a field effect transistor and a capacitor connected in series with the source-drain path thereof and across said voltage supply, the gate of the last said transistor being connected to a reference voltage.
 3. A testing device for an ionization smoke detector according to claim 2 wherein the time constant of said time constant circuit is greater than the time constant of said ionization chamber circuit. 